JPH01279680A - Light quantity detecting device - Google Patents

Abstract

PURPOSE:To optimally detect the quantity of light according to photographing status by tracking an object and executing photometry by putting emphasis on the object when the difference between the luminance of the object and that of its background is comparatively large and the object can be tracked and stopping tracking the object and switching to either center emphasized photometry or full picture average photometry when the object cannot be tracked. CONSTITUTION:A tracking frame TF and a photometric frame EF are initially set at the center of a picture, and the difference DELTAF between the level of an average video signal in the inside of the tracking frame TF and the level of another average video signal in the outside of the tracking frame TF is calculated from the outputs of area correcting circuits 56 and 58. When DELTAF is larger than a prescribed threshold TH1, namely, when the difference between the level of the video signal in the object and the level of the video signal in the background is large, the tracking frame is moved according to the position of the object, and a current mode is shifted to a tracking photometry mode in which the photometry is executed by putting emphasis on the object. When DELTAF is equal to TH1 or smaller, the tracking frame TF and the photometric frame EF are reset at the center of the picture, and DELTAF is taken in again, compared with TH1, and compared with another threshold TH2 (<TH1) when DELTAF is equal to TH1 or smaller. A center emphasized photometry mode is obtained when DELTAF is larger than TH2, and an average photometry mode is obtained when DELTAF is equal to TH2 or smaller.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light amount detection device that measures the amount of light using a video signal from an imaging means such as an image sensor.

[Conventional technology]

Video cameras automatically control the iris to adjust the amount of light depending on the shooting situation, specifically the illuminance. This exposure control device detects the amount of light from the brightness signal level in the video signal, and controls the iris so that the brightness level is always constant.

The applicant has also detected the average video signal level difference between the inside and outside of a specified area on the imaging surface, moves the specified area so that the difference is maximized, and detects the video signal from the specified area that moves in this way. A tracking photometry method has been proposed that detects the amount of light based on the following (Japanese Patent Application No. 62-277382, Japanese Patent Application No. 62-277384).

[Problem to be solved by the invention]

The above-mentioned tracking metering method focuses on the fact that the difference between the video signal level of the subject and the video signal level of the background is generally large. There is a problem that the tracking accuracy decreases.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a light amount detection device that eliminates the drawbacks of the above tracking method and operates appropriately depending on the situation even when the difference in video signal level between the subject and the background is small.

[Means to solve the problem]

The light amount detection device according to the present invention uses a first photometry method that measures the amount of light according to the average video signal level of the entire imaging surface, and a method that measures the amount of light with emphasis on the video signal within a photometric area at a predetermined position on the imaging surface. A second photometry method, and a third photometry method that tracks a subject and moves a photometry area, and measures the amount of light with emphasis on the video signal within the photometry area,
It is characterized by adaptively switching between the above three photometry methods.

[Effect]

When the difference in brightness level inside and outside the photometry area is greater than a predetermined value,
By performing photometry in the third photometry mode, the amount of light can be detected in accordance with the movement of the subject.

Furthermore, if the luminance level difference is slightly smaller than the predetermined value, center-weighted photometry is performed in the second photometry mode, and if it is even smaller than the predetermined value, whole-screen average photometry is performed. By doing so, it is possible to obtain an appropriate photometric value depending on the situation of the object to be photographed.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to the drawings.

FIG. 1 shows a block diagram of an embodiment of the present invention. In FIG. 1, 10 is a photographing lens, 12 is an aperture, 14 is an aperture control circuit that opens and closes the aperture 12, and 16 is a circuit that converts an optical image formed on the imaging surface by the lens 10 into an electrical signal, which is converted into a video signal. An image sensor such as a CCD that outputs
18 is an amplifier, 20 is a signal processing circuit that converts the output of the amplifier 18 into a luminance signal Y and two color difference signals (RY) and (B-Y), and 22 is a composite signal that converts the component signals from the signal processing circuit 20. This is an encoder that converts to .

24 is a microcomputer that controls the photometry operation in this embodiment; 26 is a microcomputer that controls the photometry operation in this embodiment; A gate circuit 28 passes the luminance signal Y corresponding to the photometry area outside the photometry frame EF (B in FIG. 3) by an inverter 30.
32.34 is the gate circuit 26 that passes through the gate circuit.
An integration circuit 36.38 integrates the output of 28 over one field period, and 36.38 normalizes the output of the integration circuit 32.34 by the area inside and outside the photometry frame to obtain the photometry area A.

40 is a coefficient multiplication circuit that multiplies the output of the area correction circuit 36 by a variable coefficient k; 42 is a variable coefficient (1) of the output of the area correction circuit 38; -k), the coefficient multiplication circuit 44 is
This is an adder that adds the outputs of the coefficient multiplication circuits 40 and 42. The aperture control circuit 14 controls the aperture 12 according to the output of the adder 44.

46 is a gate circuit that passes a luminance signal corresponding to the area inside (i.e., tracking area) of the tracking frame TF (FIG. 3) commanded by the microcomputer 24; A gate circuit 52.54 is a gate circuit 46.4 that passes a luminance signal according to the area.
56. 58 is an area correction circuit that normalizes the output of the integration circuits 52 and 54 by the area inside and outside the tracking frame.

The operation shown in FIG. 1 will be explained with reference to FIGS. 2 and 4. FIG. 2 shows a flowchart of the basic operation of the device of FIG. In FIG. 2, when the power is turned on, the tracking frame TF and the photometry frame EF are initially set at the center of the screen as shown in FIG. 3 (Sl). Next, the difference ΔF between the average video signal levels inside and outside the tracking frame TF is calculated from the output of the area correction circuits 56 and 58. ΔF is equal to the output difference of the area correction circuits 56 and 58. When ΔF is larger than a predetermined threshold THI (S
2), that is, when there is a large difference in video signal level between the subject and the background, set k in the coefficient multiplication circuit 40.42 to, for example, 0.8 (S3), move the tracking frame according to the position of the subject, and move the tracking frame to the subject. The camera shifts to a tracking photometry mode in which the photometry is performed intensively (S4). As a result, the weighting of the inside and outside of the photometry frame becomes 8:2, resulting in frame-weighted photometry. This tracking photometry mode will be described later.

When ΔF is less than or equal to THI (S2), the tracking frame TF and photometry frame EF are reset to the center of the screen (S5). continue,
Take in ΔF again and compare it with the dark value THI S6), -
○- If it is greater than Tl-11, the process proceeds to S3, and if it is less than THI, ΔF is compared with another threshold TH2 (<Tl11) (S7). When ΔF is larger than Tl2,
S6 with k in coefficient multiplication circuit 40.42 set to 0.8
Return to

At this time, the photometry frame EF is fixed at the center of the screen, and the video signal at the center of the screen is given priority, so it can be called a center-weighted photometry mode. S7
If ΔF is less than T82, k is set to 0.5, for example, and the process returns to S9. At this time, the photometry frame EF is fixed at the center of the screen, and the weighting inside and outside the photometry frame is 1:1, so that the video signal of the entire screen is considered on the average, so it can be called an average photometry mode.

FIG. 4 shows an operation flowchart of the tracking photometry mode at 34 in FIG. A simple explanation of the basic principle:
For example, shift the tracking frame up, down, left, or right by one preset section, calculate the absolute value of the difference between the average brightness levels inside and outside the tracking frame at each position, and move to the position where it is maximum. It is determined that the subject has moved, and photometry is performed with emphasis on the video signal from the tracking frame. FIG. 4 will be explained. Calculate the above ΔF and assign it to variable F1 (SIO
). The tracking frame is shifted to a one-section distribution (S11), and ΔF is taken in again and substituted into the variable F2 (S12). Fl
Compare F2 with 513), and in the case of F2≦F1,
Since it is shown that ΔF does not increase even by shifting to the right, the tracking frame is shifted to the left by one block (S14).

Then, the position of the photometry frame EF is adjusted to the position of the tracking frame TF (S15).

In steps 316 to S21, an upward shift of one section is attempted, and the metering frame EF is moved according to the result, and in steps 322 to S27, a left shift of one section is attempted, and the metering frame is moved according to the result. In steps 528 to S33, a downward shift by one section is attempted, and the photometry frame is moved in accordance with the result. S3
After 3, return to SIO.

In this example, the tracking frame and the photometry frame are set separately. This is because in the tracking mode, the tracking frame undergoes so-called wobbling and moves frequently, but if the photometry frame moves that frequently, it will look unnatural. So, if you don't mind this, you can share it. Further, the coefficients are not limited to the above numerical examples.

〔Effect of the invention〕

As can be easily understood from the above description, according to the present invention, only when the brightness difference between the subject and the background is relatively large and tracking is possible, the subject is tracked and focused metering is performed on the subject, and the brightness difference between the subject and the background is When tracking is not possible due to a small amount of light, tracking is not performed and the mode is switched to center-weighted metering or full-screen average metering depending on the stage, so it is possible to perform optimal light amount detection depending on the shooting situation.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of the configuration of an embodiment of the present invention, FIG. 2 is a flowchart of the basic operation of FIG. It is a flowchart of a mode. 10-Photographing lens 12-Aperture 14-Aperture control circuit
16-Image sensor 18-Amplifier 20-Signal processing circuit
22-Encoder 24-Microcomputer 26
．． 28.46.48-Gate circuit 30.50-Inverter 32,34,52.54--One integration circuit 36
．． 38. 56. 58-Area correction circuit 40.42
-Coefficient multiplier circuit 44-Adder

Claims (1)

[Claims] A first photometry method that measures the amount of light according to the average video signal level of the entire imaging surface, a second photometry method that measures the amount of light with emphasis on the video signal within a photometry area at a predetermined position on the imaging surface; A third method that tracks and moves the photometric area and measures the amount of light with emphasis on the video signal within the photometric area.
1. A light amount detection device comprising: a photometry method; and adaptively switching between the three photometry methods.